HARRISBURG, Pa. - Pennsylvania's state Republican Party committee members are gathering this weekend as a clash brews over whether or who to endorse in the crowded field of candidates vying for the party's U.S. Senate nomination to contest Democrat Bob Casey's re-election bid this year.

Six candidates are running , only one of whom has held public office or run statewide before , and a majority of state committee members voting at Saturday's meeting in Hershey will be required to give the party's blessing in the run-up to the April 24 primary.

The party's endorsement means the winner will have its backing and access to its considerable resources to win the primary campaign. A contested primary is assured: Several candidates say they'll run even without the endorsement, and all may run if the committee votes not to endorse.

While candidates continued Friday to court committee members to win endorsement votes, a couple candidates nonetheless said they oppose an endorsement vote and Tea Party-aligned groups were calling for an open primary as a matter of principle.

"The Republican State Committee doesn't self-police," said Katy Abram, a committee member of the Lebanon County Republican party who founded the Lebanon 9-12 Project. "They tend to stick with the guy with the name, whether he's principled, whether he stands for the party platform or not."

U.S. Sen. Pat Toomey is not endorsing, but Gov. Tom Corbett is pressing state committee members to support his choice, Chester County entrepreneur Steve Welch, who flirted with running for two different U.S. House seats in 2010 but dropped out in deference to party-backed candidates.

Welch finished third in straw voting in January by various state committee caucuses. The most votes were won by Washington County entrepreneur Tim Burns, who lost two elections for the U.S. House in 2010, followed by former coal industry executive Tom Smith of Armstrong County, a Democrat-turned-Republican who has never run for office before but has invested $5 million of his own money into his campaign.

Even after the governor's support for Welch became public knowledge, Welch lost straw votes by the southwestern and northwestern Pennsylvania caucuses, and his home-turf southeastern caucus decided not to vote. Welch has been criticized for briefly changing his registration to Democrat so he could vote for Barack Obama in the 2008 Democratic presidential primary

Welch's advisers were making no predictions Friday.

"We'll see what happens tomorrow," said spokesman John Brabender. "Clearly, he's going in with a lot of momentum, but I don't think anyone will know until the final vote is taken."

Other GOP Senate candidates include former state Rep. Sam Rohrer of Berks County, who unsuccessfully challenged Corbett in the 2010 GOP gubernatorial primary; Bucks County manufacturing executive David Christian, who ran unsuccessfully for Congress twice; and lawyer Mark Scaringi of Cumberland County.

Rohrer and Scaringi say they oppose an endorsement and, like Smith, plan to run regardless of who the party endorses.

The difference at the state committee meeting is that votes are public, while straw votes are secret.

To start, the committee members will vote Saturday on whether to endorse. If a majority votes to endorse, then the committee will hold endorsement votes in rounds, with the lowest vote-getter dropping out after each round until a candidate gets at least 50 percent. Enough abstentions could also keep candidates from getting a majority, meaning no endorsement is given.